The present invention relates to an internal combustion engine, and more particularly to a decoupled internal combustion engine whereby the mixing and compressing of air and fuel occurs within a first cylinder and the combusting and exhausting occurs within a second cylinder.
The engine development process has often involved making decisions between competing engine characteristics, including fuel efficiency, power output, physical size, emission characteristics, reliability, and durability to name a few. In particular, emission characteristics are one criteria that are often evaluated by organizations like the Environmental Protection Agency (EPA). For instance, if some emission levels, such as nitrous oxides (NOx), hydrocarbons (HC), carbon monoxide (CO) or particulate matter are too high for an engine, the engine may require expensive exhaust treatments such as a catalytic converter. In other instances, the engine might not be certified for operation or sale if it has poor emissions characteristics. As a result, engine emissions should be carefully considered during the engine development process. Some issues surrounding engine development regarding emissions characteristics are described below.
Carbon monoxide and NOx emissions (including both NO and NO2) are formed during combustion. Carbon monoxide generally results when combustion occurs with an air and fuel mixture that has more fuel than the stochiometric reaction requires (also known as a xe2x80x9crichxe2x80x9d mixture). To address carbon monoxide concerns, most engines attempt to operate with stochiometric or lean (less fuel than stochiometric) air and fuel mixtures. However, some pockets of fuel rich zones will typically still exist in the air and fuel mixtures of conventional engines. These pockets can result in carbon monoxide production. Conversely, NOx emissions are high when the air and fuel mixtures are lean or near stochiometric values. Techniques used to address NOx formation include the recirculation of exhaust gases into fresh air and fuel mixtures.
Among other causes, Hydrocarbon (HC) emissions can result from incomplete combustion or unburned fuel passing through a power cylinder during a period of intake and exhaust valve overlap. Cylinders of conventional engines often provide areas where it is difficult to sustain combustion, such as in the crevices between a piston and a cylinder wall. Additionally, most fuel injection systems cannot provide fuel that is completely evaporated before combustion begins. Fuel may also cling to the walls of a cylinder after it has been injected, forming a wet sheet of fuel that does not burn. This often leads to incomplete combustion in at least portions of a combustion chamber resulting in hydrocarbon emissions. Hydrocarbon emissions are often worse when an engine is first started, as the engines are typically cold and complete evaporation of fuel is difficult to support.
Both in diesel and spark-ignition engines, the ratio of the fuel to air is not the same throughout the cylinderxe2x80x94thus not stochiometricxe2x80x94due in part to poor mixing. Some part of the fuel/air mixture is fuel rich and some part is oxygen rich (i.e., lean). The crown of the piston (i.e., the top of the piston), the injection angle, and valve size and location, etc. are varied to control the flow of injected fuel/air mixture, but the problem still persists. This non-stochiometric ratio may limit the maximum compression ratio of the engine, which controls the flame propagation speed and the combustion chemistry.
Another problem of conventional four-stroke spark-ignition engines is the knocking of the engine. This knocking problem limits the maximum compression ratio of conventional IC engines and thus, the power efficiency of the engines. This limiting compression ratio, in turn, determines the volume of the cylinder that still contains the hot combustion product when the piston is at the highest position of its compression stroke. Knocking is a result of self-ignition or auto-ignition. To prevent knocking, the most desirable combustion process in the power cylinder of spark-ignition IC engines is the one where a flame sheet propagates from the ignition point outward at a high compression ratio. Because of the expansion of the gas behind the flame front, the unburned fuel vapor and air experiences high pressure and temperature before the flame front reaches the unburned region. When the pressure and temperature of the unburned fuel-vapor/air mixture are high enough, the mixture can self-ignite (i.e., auto-ignition), causing a rapid rise in pressure, which induces vibration of the cylinder walls and audible knocks. This process is accelerated when there is enough time for sufficient auto-ignition precursors to form. Two mechanisms control xe2x80x9cknockingxe2x80x9d: the formation of precursors and the temperature rise that accelerate the flame propagation rate. At high engine speeds knocking may not be a problem since there is less time available for the precursors to form. On the other hand, as engine speed increases, there is less heat loss from the gases so that gas temperatures will be higher. This accelerates the precursor formation rate so that less time is required to form a concentration high enough for auto-ignition to occur. As a result of these two competing effects, some engines show knocking at high speeds, whereas some at low speeds. Knocking can be severe when the fuel-vapor/air mixture is at its stochiometric ratio. This problem has been solved in current engines in two expensive ways: the use of anti-knock additives and the lowering of the compression ratio. To prevent auto-ignition, high-octane fuelxe2x80x94a mixture of many hydrocarbons with high-octane additivesxe2x80x94is used in high compression engines. If knocking persists even with the use of high-octane gasoline, it is eliminated by changing the ignition time to ignite the fuel-vapor/air mixture at a lower pressure (thus at a lower compression ratio) when the piston has moved downward from its highest position. This lowers fuel efficiency.
Conventional methods of developing products, and specifically internal combustion engines, often lead to lengthy development cycles and consequently high cost due to the iterative nature of such methods. For example, an engine designer may make a modification to one component of an engine which, in turn, requires him to make many other modifications in other already designed and tested components of the engine. Making such a change may require re-evaluating the previously tested components, thereby adding cost and time to the development process.
The inventors of the present invention have found that the use of an axiomatic design approach offered a workable methodology to design an engine that addresses at least some of the above-mentioned issues. Using an axiomatic design approach can provide a process to design an engine that allows a designer to achieve an engine with the characteristics he or she wants by providing a clear description of how the designer can achieve the characteristics. Once the engine designer understands the design needs, the understanding is transformed into a minimum set of specifications, which are defined as functional requirements (FR""s), that adequately describe xe2x80x9cwhat the designer wants to achievexe2x80x9d to satisfy the design needs. The descriptor of xe2x80x9chow the designer will achieve the needsxe2x80x9d is articulated in the form of design parameters (DP""s).
A basic postulate of the axiomatic design approach used to design the internal combustion engine described herein, is that there are fundamental axioms that govern the design process. There are two primary axioms associated with the axiomatic design approach.
The first axiom is called the independence axiom. It states that the independence of functional requirements (FR""s) should be maintained, where FR""s are defined as the minimum set of independent requirements that characterize the design goals. A set of FR""s is the description of design goals. The independence axiom states that when there are two or more FR""s, the design solution should be such that each one of the FR""s can be satisfied without affecting the other FR""s. This means an engine designer has to choose a correct set of DP""s to be able to satisfy the FR""s and maintain their independence.
The second axiom is called the information axiom, and it states that among those designs that satisfy the independence axiom, the design that has the smallest information content is the best design. Because the information content is defined in terms of probability, the second axiom also states that the design that has the highest probability of success is the best design.
The independence axiom requires that the functions of the design be independent (i.e. decoupled) from each other, and not that the physical parts be independent. The second axiom suggests that physical integration is desirable to reduce the information content if the functional independence can be maintained.
Conventional internal combustion (IC) enginesxe2x80x94both spark-ignition engines and diesel enginesxe2x80x94are coupled designs from the axiomatic design point of view. In an ideally designed product, the function of the product is specified in terms of functional requirements (FRs) and constraints (C), which are satisfied exactly as specified by choosing a correct set of design parameters (DPs). When a wrong set of DPs are chosen, a coupled design results. In a coupled design, the functional requirements (FRs) of a systemxe2x80x94e.g., enginexe2x80x94are not independent from each other and therefore, each time a design parameter is changed to vary one of the FRs, all other FRs change, making it difficult to satisfy all FRs within the desired range. Hence, in a coupled design, FRs must be compromised to get a minimally acceptable performance rather than making the system behave as originally envisioned and specified to achieve the ultimate results desired.
The basic causes for coupling are different between four-stroke cycle engines and two-stroke cycle engines, and also between spark-ignition and diesel engines. However, in all current designs, the basic functions of the engines are coupled to each other and therefore, cannot be controlled precisely. In the case of most commonly used spark-ignition IC engines, the fuel is injected using a fuel injector into the intake manifold or inlet port (port fuel injection) outside of the combustion cylinder, which evaporates and mixes with air and flows into the cylinder during the downward stroke of the piston in the cylinder. However, part of the fuelxe2x80x94either in vapor or liquid phasexe2x80x94remains in the manifold and does not combust in the cylinder. This unburned fuel is carried out of the intake manifold when the hot combustion product is exhausted from the cylinder. When the unburned fuel mixes with the hot exhaust gas, it partially oxidizes.
Further details of the axiomatic design approach as discussed herein can be found in xe2x80x9cThe Principles of Designxe2x80x9d by Nam P. Suh, Oxford University Press, 198 Madison Avenue, New York, N.Y. (1990), and xe2x80x9cAxiomatic Design, Advances and Applicationsxe2x80x9d by Nam P. Suh, Oxford University Press, 198 Madison Avenue, New York, N.Y. (2001) both of which are incorporated by reference in their entirety.
In using the axiomatic design approach, the engine of the present invention has been designed such that the functional requirements of the engine design are satisfied independent of one another by various design parameters. This allows design changes to be implemented easily in the engine. This also leads to the engine of the present invention being able to achieve lower emission levels than conventional engines. Several features of various embodiments of the present invention that improve the emissions characteristics of the engine are now described. An embodiment of the engine may include one or more features, each independently or in combination.
In particular, the invention disclosed herein creates a decoupled enginexe2x80x94an engine whose functional requirements (FRs) can be satisfied independently of other FRs when the design parameters are varied in a given sequence. A goal is to improve the fuel efficiency as well as to eliminate (or reduce) the use of costly exhaust treatments, such as a catalytic converter. The Suh engine has two kinds of cylinders: power cylinders (referred to as Cylinder P or PC in this write-up) where the combustion takes place, and fuel/oxidizer conditioning/mixing cylinders (Cylinder C or MC) where fuel vapor and air are mixed and homogenized. The engine of the present invention will deliver at least the same amount of power as conventional four-stroke cycle spark-ignition engines without making the engine larger, since the power cylinders operate with a power stroke during every crankshaft revolution. It should produce more complete combustion productsxe2x80x94without the use of the catalytic converter currently used in IC enginesxe2x80x94because substantially all the injected fuel undergoes combustion and minimal, if any, unburned hydrocarbons are exhausted. Liquid fuel, which is one of the causes for incomplete combustion, does not enter into the power cylinder, always remaining in the mixing and conditioning cylinder (Cylinder C). The general concept of the engine of the present invention can be extended to other engine configurations, including diesel engines and other forms of spark-ignition engines.
These IC engines should satisfy the following functional requirements (FRs):
FR1=Measure the right amount of fuel for each combustion cycle
FR2=Evaporate fuel
FR3=Measure the right amount of air (i.e., oxidizer) for each combustion cycle
FR4=Mix the vaporized fuel with the oxidizer
FR5=Inject the mixture into the combustion chamber at a preset pressure
FR6=Ignite the fuel/oxidizer mixture
FR7=Deliver the power
FR8=Exhaust the combustion product
FR9=Minimize frictional loss
FR10=Control the emission of NOx, hydrocarbons, and CO
These highest-level FRs should be decomposed when the design parameters (DPs) chosen to satisfy are not detailed enough to be implemented.
The engine of the present invention uses two kinds of cylinders: a power cylinder (Cylinder P) and a fuel/air mixing and conditioning cylinder (Cylinder C). Cylinder C is used to satisfy FR2, FR3, FR4 and FR5. The function of Cylinder C is to prepare the fuel/air mixture for the power cylinder in which combustion takes place. The present invention employs the separation of functions using one cylinderxe2x80x94Cylinder Cxe2x80x94to meter the fuel and air, and then mix the fuel vapor with air, and the other cylinderxe2x80x94Cylinder Pxe2x80x94to combust the mixture and deliver power. This arrangement together with other features can minimize the emission of NOx, hydrocarbons, and CO and increase fuel efficiency.
According to one aspect of the invention an internal combustion engine is provided. The engine comprising a cylinder block having a first cylinder and a second cylinder, a first piston disposed in the first cylinder, and adapted to reciprocate through a first swept volume for substantially completing an intake stroke and a compression stroke within the first cylinder to form a homogeneous air and fuel charge. The engine also has a second piston disposed in the second cylinder, and adapted to reciprocate through a second swept volume for substantially completing a power stroke and an exhaust stroke within the second cylinder. Furthermore, the engine has a crankshaft rotatably mounted within the cylinder block about an axis of rotation. Additionally, the engine has a first connecting rod having a first end operably coupled to the first piston and a second end operably coupled to the crankshaft such that the second end of the first connecting rod is adapted to rotate with the crankshaft about the axis of rotation. A second connecting rod is also included in the engine, the second connecting rod has a first end operably coupled to the second piston and a second end operably coupled to the crankshaft such that the second end of the second connecting rod is adapted to rotate with the crankshaft about the axis of rotation. Furthermore, a conduit in fluid communication exists between the first swept volume and the second swept volume for delivering substantially all of the air and fuel charge from the first swept volume to the second swept volume. The conduit has a first portion opening into the first cylinder and a second portion opening into the second cylinder. The first portion is selectively closable for closing fluid communication between the first swept volume and the conduit. The second portion is selectively closable for closing fluid communication between the second swept volume and the conduit. The second portion is adapted to open out of phase with the first portion.
According to another aspect of the invention an internal combustion engine is provided. The engine comprising a cylinder block having a first cylinder and a second cylinder, a first piston disposed in the first cylinder, and adapted to reciprocate through a first swept volume for substantially completing an intake stroke and a compression stroke within the first cylinder to form a homogeneous air and fuel charge. The engine also has a second piston disposed in the second cylinder, and adapted to reciprocate through a second swept volume for substantially completing a power stroke and an exhaust stroke within the second cylinder. The second swept volume is smaller than the first swept volume. Furthermore, the engine has a crankshaft rotatably mounted within the cylinder block about an axis of rotation. Additionally, the engine has a first connecting rod having a first end operably coupled to the first piston and a second end operably coupled to the crankshaft such that the second end of the first connecting rod is adapted to rotate with the crankshaft about the axis of rotation. A second connecting rod is also included in the engine, the second connecting rod has a first end operably coupled to the second piston and a second end operably coupled to the crankshaft such that the second end of the second connecting rod is adapted to rotate with the crankshaft about the axis of rotation. Furthermore, a conduit in fluid communication exists between the first swept volume and the second swept volume for delivering substantially all of the air and fuel charge from the first swept volume to the second swept volume. The conduit has a first portion opening into the first cylinder and a second portion opening into the second cylinder. The first portion is selectively closable for closing fluid communication between the first swept volume and the conduit. The second portion is selectively closable for closing fluid communication between the second swept volume and the conduit.
According to yet another aspect of the invention an internal combustion engine is provided. The engine comprising a cylinder block having a first cylinder and a second cylinder, a first piston disposed in the first cylinder, and adapted to reciprocate through a first swept volume for substantially completing an intake stroke and a compression stroke within the first cylinder to form a homogeneous air and fuel charge. The engine also has a second piston disposed in the second cylinder, and adapted to reciprocate through a second swept volume for substantially completing a power stroke and an exhaust stroke within the second cylinder. Furthermore, the engine has a crankshaft rotatably mounted within the cylinder block about an axis of rotation. Additionally, the engine has a first connecting rod having a first end operably coupled to the first piston and a second end operably coupled to the crankshaft such that the second end of the first connecting rod is adapted to rotate with the crankshaft about the axis of rotation. A second connecting rod is also included in the engine, the second connecting rod has a first end operably coupled to the second piston and a second end operably coupled to the crankshaft such that the second end of the second connecting rod is adapted to rotate with the crankshaft about the axis of rotation. Furthermore, a conduit in fluid communication exists between the first swept volume and the second swept volume for delivering substantially all of the air and fuel charge from the first swept volume to the second swept volume. The conduit has a first portion opening into the first cylinder and a second portion opening into the second cylinder. The first portion is selectively closable for closing fluid communication between the first swept volume and the conduit. The second portion is selectively closable for closing fluid communication between the second swept volume and the conduit. The engine also has an exhaust passage in fluid communication with the second swept volume. The passage is selectively closable, the exhaust passage adapted to remain open for a period of time while the second portion is open.
According to yet another aspect of the invention, an internal combustion engine is disclosed. The engine having a cylinder block with a first cylinder, a second cylinder, and a third cylinder. A first piston is disposed in the first cylinder, and adapted to reciprocate through a first swept volume for substantially completing an intake stroke and a compression stroke within the first cylinder to form a homogenous air and fuel charge. A second piston is disposed in the second cylinder, and adapted to reciprocate through a second swept volume for substantially completing a power stroke and an exhaust stroke within the second cylinder. A third piston is disposed in the third cylinder, and adapted to reciprocate through a third swept volume for substantially completing a power stroke and an exhaust stroke within the third cylinder. Also a crankshaft is rotatably mounted within the cylinder block about an axis of rotation. Further, a first connecting rod has a first end operably coupled to the first piston and a second end operably coupled to the crankshaft such that the second end of the first connecting rod is adapted to rotate with the crankshaft about the axis of rotation. A second connecting rod has a first end operably coupled to the second piston and a second end operably coupled to the crankshaft such that the second end of the second connecting rod is adapted to rotate with the crankshaft about the axis of rotation. A third connecting rod has a first end operably coupled to the third piston and a second end operably coupled to the crankshaft such that the second end of the third connecting rod is adapted to rotate with the crankshaft about the axis of rotation. A first conduit is in fluid communication between the first swept volume and the second swept volume. A second conduit is in fluid communication between the first swept volume and the third swept volume. Additionally, a first closable portion exists for closing fluid communication between the first swept volume and the first conduit and a second closable portion exists for closing fluid communication between the first swept volume and the second conduit.
According to an additional aspect of the invention, an internal combustion engine exists that has a cylinder block having a first cylinder, a second cylinder, and a third cylinder. A first piston is disposed in the first cylinder, and adapted to reciprocate through a first swept volume for substantially completing an intake stroke and a compression stroke within the first cylinder to form a homogeneous air and fuel charge. A second piston is disposed in the second cylinder, and adapted to reciprocate through a second swept volume for substantially completing a power stroke and an exhaust stroke within the second cylinder. A third piston is disposed in the third cylinder, and adapted to reciprocate through a third swept volume for substantially completing a power stroke and an exhaust stroke within the third cylinder. Additionally, a first conduit provides fluid communication between the first swept volume and the second swept volume. A second conduit provides fluid communication between the first swept volume and the third swept volume. A first closable portion exists for closing fluid communication between the first swept volume and the first conduit. A second closable portion exists for closing fluid communication between the first swept volume and the second conduit. A third closable portion exists for closing fluid communication between the first conduit and the second swept volume. Additionally, a fourth closable portion exists for closing fluid communication between the second conduit and the third swept volume.
According to still another aspect of the invention, an internal combustion engine is disclosed. The engine has a pair of cylinders each having a reciprocating piston connected to a common crank shaft by a connecting rod. The rods are sized and positioned to maintain constant phase angles. One of the cylinders is adapted for an air and fuel intake and a compression strokes only, and the other of the cylinders adapted for power and exhaust strokes only. A conduit exists for transfer of gases from the one into the other cylinder after the compression stroke. The conduit has means for isolating gases in the conduit intermediate the compression and power strokes. Furthermore, the conduit is positioned above at least a portion of the cylinders whereby any volume of liquefied fuel transferred from the one chamber to the transfer port is minimized.
Still, according to an additional aspect of the invention, an internal combustion engine is disclosed. The engine comprising a first cylinder for receiving air and fuel to be mixed in the first cylinder and compressed within the first cylinder by a first piston driven by a first connecting rod, thereby creating a compressed air and fuel charge. The engine also has a crankshaft that drives the first connecting rod, the connecting rod having an end operably connected to the crankshaft that follows a circular orbit. A chamber is in selectable fluid communication with the first cylinder and is adapted to receive substantially all of the compressed air and fuel charge while retaining any liquid fuel in the first cylinder. The chamber is further adapted to contain the compressed air/fuel charge as a first portion of a compressed air and fuel mixture and to maintain the compressed air fuel mixture at an elevated, operating pressure range. Additionally, a second cylinder is in selectable fluid communication with the chamber, and is adapted to receive a second portion of the compressed air/fuel mixture as a second compressed air/fuel charge. The second cylinder is also adapted to combust the second compressed air and fuel charge to drive a second piston connected to a second connecting rod. Wherein the second connecting rod has an end operably connected to the crankshaft and the second connecting rod drives the crankshaft and the end of the second connecting rod in a circular orbit.
In another aspect of the invention, a method of deriving power from combustible fuel is provided. The method comprising the steps of admixing and compressing vaporized fuel in a first chamber, into admixed gases. Then compressing the admixed gases in the first chamber and segregating the admixed gases from liquid residue in the first chamber. Thereafter isolating the admixed gases in a conduit and then transferring the admixed gases free of any significant liquids into a second chamber. Igniting the admixed gases within the second chamber and then driving a piston to deliver power.
In another aspect of the invention a method of operating an internal combustion engine is provided. The method comprises providing air and fuel to a first cylinder and mixing the fuel and the air within the first cylinder. Then driving a piston in the first cylinder with a connecting rod, the connecting rod having an end operably connected to a crankshaft, and the end following a circular orbit as it is driven by the crankshaft. The air and the fuel is then compressed within the first cylinder with the first piston to create a compressed air/fuel charge. Substantially all the compressed air/fuel charge is delivered to a chamber while retaining any liquid fuel in the first cylinder. The chamber containing the compressed air/fuel charge exists as a first portion of a compressed air/fuel mixture and maintains the compressed air fuel mixture within an elevated, operating pressure range. A second portion of the compressed air/fuel mixture is delivered to a second cylinder as a second compressed air/fuel charge, while maintaining a remaining portion of the compressed air/fuel mixture in the accumulator within the elevated, operating pressure range. The second compressed air/fuel charge is combusted within the second cylinder to drive a second piston within the second cylinder. The second piston drives a second connecting rod, which drives the crankshaft with the second connecting rod. An end of the second connecting rod is operably connected to the crankshaft and following a circular orbit as it drives the crankshaft.
Various embodiments of the present invention provide certain advantages and overcome certain drawbacks of prior internal combustion engines. Embodiments of the invention may not share all of the same advantages, and those that do may not share them under all circumstances. This being said, the present invention provides numerous advantages including improved emission characteristics.
Further features and advantages of the present invention, as well as the structure of various embodiments, are described in detail below with reference to the accompanying drawings.